1. Field of the Invention
This invention relates to a flash control device and a flash control system for wirelessly controlling a flash device through optical communication.
2. Description of the Related Art
Japanese Unexamined Patent Application Publication No. Hei 11-190872 has proposed a device that changes the light emission amount of the optical communication in accordance with the amount of information to be transmitted. It has also proposed a device that determines the charge status of a capacitor and controls the light emission amount of the optical communication in accordance with the determined status.
It is desirable that devices of these types have a long controllable wireless distance because a longer controllable distance leads to a wider use range of the devices. It is, therefore, desirable that signals can travel as far as possible. To lengthen the reachable distance of the signals, the intensity of the optical signals need to be high and hence the optical signals need to be emitted at intensity as high as possible.
However, in a case where a flash emitting part for photographing is also used as an optical signal transmitting part, there has been a problem that heightening the intensity of the optical communication results in reducing the power available during photographing, which reduces the amount of light emission at the photographing.
According to the conventional technique for controlling slave flash devices (wireless electronic flashes) by use of preliminary light emission, a master flash device (main electronic flash) has to consume a large amount of power for the preliminary light emission and for generation of small-light-emission pulses in order to communicate with the slave flash devices, resulting in significantly reduced power left for main light emission. Actually, it is more accurate to say that minimum light emission power required for a main flash emission of the master flash device is secured first and then the power required for the preliminary light emission and small-light-emission pulses for the communication is secured from the remaining power. Consequently, the light amount of the small-light-emission pulses for the communication has to be significantly reduced, so that the distance in which the slave flash devices are receivable of the small-light-emission pulses for the communication is limited to a short distance.
Therefore, in the case of a long distance between the master flash and the slave flash devices or of communicating by use of light emission pulses reflected from peripheral objects or the like because no lines of sight therebetween are secured due to its surrounding environment at the photographing, the slave flash devices cannot obtain sufficient reception intensity resulting in failure of communication, or may result in a malfunction due to a poor communication. Conventionally, it is impossible to flexibly change the optical communication intensity by properly determining whether the light emission intensity for optical communication is increasable or has to be increased.
The technique for determining the charge status of the capacitor disclosed in the foregoing Japanese Unexamined Patent Application Publication No. Hei 11-190872 is intended for preventing occurrence of a failure in optical signal emission by reducing the light mission amount during a low charge voltage. This way of control, however, may cause the slave flash devices to be unstable in operation such as a malfunction or a failure in emitting slave light due to a lack of light emission amount for the optical signals.
The foregoing Japanese Unexamined Patent Application Publication No. Hei 11-190872 describes the light emission during the communication, yet it does not consider the illumination during a main light emission. Particularly, for a small-sized or built-in camera flash device or the like with a small power capacity (capacitor value), the optical communication is unfeasible if a large amount of power is consumed for the illumination during the main light emission; to the contrary the illumination amount thereof becomes insufficient or the main light emission is unfeasible if a large amount of power is consumed for the optical communication.
Then, it is an object of the present invention to provide a flash control device and a flash control system that are able to establish proper intensities of optical communication in accordance with various conditions at the time of photographing.
It is another object of the present invention to provide a flash control device and a flash control system that are able to appropriately control slave flash devices even when a master flash device has small power capacity and far from the slave flash devices, or communication between the master flash device to the slave flash devices has to be made by light emission pulses reflected from a peripheral object or the like because the surrounding environment obstructs a line of sight from the master flash device to the slave flash devices at the time of photographing.
The present invention will be described below.
(1)
A flash control device of the present invention controls a slave flash device that emits upon receiving an operational instruction via optical communication. The flash control device includes: a signal emitting part for emitting an optical signal used for the optical communication; a power determining part for determining a state of supply of power to be used for the light emission of the signal emitting part; and a communication intensity deciding part for deciding, based on a determination result from the power determining part, the intensity of the optical signal to be emitted by the signal emitting part.
(2)
In the flash control device of the above item (1), the signal emitting part is preferably able to emit a flash serving as illumination at the time of photographing.
(3)
In the flash control device of the above item (2), the communication intensity deciding part preferably increases the signal intensity of the optical signal emitting part when illumination is set to be provided at the time of photographing.
(4)
In the flash control device of the above item (1), the communication intensity deciding part preferably increases the intensity of the optical signal to be emitted by the optical signal emitting part when the flash control device is provided with an external power supply device in its exterior for additional supply of the power to be used for the light emission of the signal emitting part.
(5)
In the flash control device of the above item (4), the signal emitting part is preferably able to emit a flash serving as illumination at the time of photographing.
(6)
In the flash control device of the above item (5), the communication intensity deciding part preferably increases the signal intensity of the optical signal emitting part when no illumination is set to be provided at the time of photographing.
(7)
Another flash control device of the present invention controls a slave flash device that emits a flash upon receiving an operational instruction via optical communication. The flash control device includes: a signal emitting part for emitting an optical signal used for the optical communication; a slave flash determining part for determining whether or not the slave flash device has emitted preliminary slave light, in accordance with the optical signal emitted by the signal emitting part; and a communication intensity deciding part for increasing the intensity of the optical signal to be emitted by the optical signal emitting part when the slave flash determining part determines that the preliminary slave light has not been emitted.
(8)
In the flash control device of the above item (7), the signal emitting part is preferably able to emit a flash serving as illumination at the time of photographing.
(9)
In the flash control device of the above item (8), the communication intensity deciding part preferably increases the signal intensity of the optical signal emitting part when no illumination is set to be provided at the time of photographing.
(10)
Another flash control device of the present invention controls a slave flash device that emits a flash upon receiving an operational instruction via optical communication. The flash control device includes: a signal emitting part for emitting an optical signal used for the optical communication; a photometry part for measuring the brightness of a subject field; and a communication intensity deciding part for deciding, based on a measurement result from the photometry part, the intensity of the optical signal to be emitted by the signal emitting part.
(11)
A flash control system of the present invention includes: a photographing device; a slave flash device that emits a flash upon receiving an operational instruction via optical communication; and a signal emitting part for emitting an optical signal used for the optical communication. The signal emitting part is attached to the photographing device and changeably functions as a light/signal emission device that can emit a flash serving as illumination at the time of photographing and a dedicated signal emission device that emits the optical signal to only give an operational instruction to the slave flash device. The photographing device sets the intensity of the optical signal to be emitted by the dedicated signal emission device to be greater than the intensity of the optical signal to be emitted by the light/signal emission device.
(12)
Another flash control system of the present invention includes: a photographing device; a slave flash device that emits a flash upon receiving an operational instruction via optical communication; and a signal emission device attached to the photographing device and having a signal emitting part for emitting an optical signal used for the optical communication, and it further includes: a photometry part provided in the photographing device and/or in the signal emission device for measuring the brightness of a subject field; and a communication intensity deciding part for deciding, based on a measurement result from the photometry part, the intensity of the optical signal to be emitted by the signal emitting part.
(13)
Another flash control device of the present invention controls a slave flash device that emits a flash upon receiving an operational instruction via optical communication. The flash control device includes: a signal emitting part capable of emitting an optical signal used for the optical communication and of emitting a flash serving as illumination at the time of photographing; and a communication intensity deciding part for deciding the intensity of the optical signal to be emitted by the signal emitting part. When the signal emitting part does not illuminate at the time of photographing, the communication intensity deciding part sets the signal intensity of the optical signal emitting part to be greater than when the signal emitting part illuminates at the time of photographing.
(14)
Another flash control device of the present invention controls a slave flash device that emits a flash upon receiving an operational instruction via optical communication. The flash control device includes a signal emitting part capable of emitting an optical signal used for the optical communication and of emitting a flash serving as illumination at the time of photographing; and a communication intensity deciding part for deciding the intensity of the optical signal to be emitted by the signal emitting part. When the slave flash device is set to be controlled, the communication intensity deciding part inhibits the signal emitting part from illuminating at the time of photographing.
(15)
In the flash control device of the above item (14), the signal emitting part is preferably a flash device built in the photographing device.
(16)
In the flash control device of the above item (14), preferably the communication intensity deciding part does not inhibit the signal emitting part from illuminating at the time of photographing when the photographing device is provided with an external flash device as the signal emitting part which has a light emission capacity greater than a predetermined value, even when the slave flash device is set to be controlled.